There are known whole body and partial body MRI systems (e.g., superconductive, resistive having cylindrical symmetry, and iron core magnets having permanent magnet and electromagnet excitation) having an imaging area in the central part of the magnet. The imaging area or region in the central part of these known magnets is generally not accessible for medical personal when a patient is placed in the magnet for MRI. In addition, the geometry of those type of prior art designs of superconductive magnets are typically limited in terms of field strength at about 1.5-2 T, which is sufficient for obtaining images of most body tissue and for spectroscopy. However, a higher field strength up to 3-5 T, and even higher, is required to image using phosphor NMR signals of tissue or to provide more precise spectroscopy. Whole Body magnets providing such high field strength are technically difficult to achieve with the present state of the art of solenoidal superconductive magnets.
An iron core magnet described by Pulyer in U.S. Pat. No. 5,049,848, which may be particularly useful for MRI mammography, has magnet geometry that may conceptually provide access to part of body placed into the imaging space, i.e. air gap or imaging volume. However, iron core magnets of that type are limited in field strength due to iron core saturation limits.
Accordingly, new magnet designs are desired that provide high field strength and that provide access for medical personnel, particularly for whole body imaging.